Calculate the Length to Height Ratio of a Flatfish

Instructions are in the task pane to the left. Complete and submit each task one at a time.

This code sets up the activity.

flatFish = imread("./images/flatfish.jpg");

% Create mask with local function at bottom of script

fishBW = fishMask(flatFish);

imshowpair(flatFish, fishBW, "montage")

Task 1

You only need to work with the connected component representing the fish, which is the largest one.

You can use the bwpropfilt function to keep the n largest or smallest objects when sorted by attrib.

BW2 = bwpropfilt(BW,attrib,n,keep);

Specify keep as either "largest" or "smallest".

fishOnly = bwpropfilt(fishBW, "Area", 1, "largest");

imshow(fishOnly)

Task 2

The regionprops function works on binary images as well as on label matrices. The syntax is the same.

stats = regionprops(output,BW,props)

output specifies the type of stats and is either "struct" or "table". BW is a binary image, and props is a string array specifying the properties to return.

fishOrient = regionprops("table", fishOnly, "Orientation")
fishOrient = table table 
 Orientation
1-4.0427

	Orientation
1	-4.0427

Task 3

You can use imrotate to rotate an image counterclockwise.

I2 = imrotate(I,angle);

angle = fishOrient.Orientation;
fishRot = imrotate(flatFish, -angle);

Task 4

BWrot = imrotate(fishOnly, -angle);

rotOverlay = imoverlay(fishRot, BWrot);

imshow(rotOverlay)

Task 5

fishBB = regionprops("table", BWrot, "BoundingBox")
fishBB = table table 
 BoundingBox
1201.5000174.50001237823
fishBox = fishBB.BoundingBox
fishBox = 1×4
103 ×
    0.2015    0.1745    1.2370    0.8230

	BoundingBox
1	201.5000	174.5000	1237	823

Task 6

You can display a bounding box over an image by passing it as the position to the rectangle function.

hold on

rectangle("Position",pos,"Name",Value)

hold off

pos is the position of the rectangle. With name-value pairs, you can specify properties of the rectangle like "EdgeColor" and "LineWidth".

hold on

rectangle("Position", fishBox, "LineWidth", 5)

hold off

Task 7

The bounding box is a 4-element vector, [x y w h] where x and y are the coordinates of the bottom left corner of the box and w and h are the width and height of the box.

wt = fishBox(3);
ht = fishBox(4);
 
ratio = wt / ht
ratio = 1.5030

function fishBW = fishMask(flatFish)
    % use texture segmentation and smoothing 
    % to segment camouflaged fish
    
    fishGray = rgb2gray(flatFish);
    fishSTD = stdfilt(fishGray);
    fishSTD = rescale(fishSTD);
    
    filterSize = [15 15];
    fishFilt = medfilt2(fishSTD, filterSize);
    
    fishBW = ~imbinarize(fishFilt);
end